Steel



Patented Dec. 5, 1939 UNITED STATES STEEL Oscar E. Harder, Columbus, Ohio, assignor to Inland Steel Gompany, Qhicago, Ill., a corporation of Delaware No Drawing. Application August 15, 1938, Serial No. 224,963

6 Claims.

The invention relates to steel. It is direct-c more particularly to the improvement of those steels which, in commerce, are commonly referred to as alloy steels, although my invention is not necessarily limited thereto.

The principal object of my invention is to improve the machinability of the said alloy steels. Another object of my invention is to impart to the said alloy steels lower frictional resistance or coefficients of friction than other steels of otherwise similar composition but not containing lead.

In the prior art, the practice most generally resorted to for the purpose of improving the machinability of steel is the addition of sulfur to the steel. For example, certain "free cutting" steels have attained a well established and recognized classification in the steel industry. The Society of Automotive Engineers recognizes this special class of steel and has provided standard specifications for their chemical composition. Sometimes, selenium is used, though the cost thereof is somewhat prohibitive. Normally, where sulfur or selenium'is used for improving the machinability of the steel, they are introduced in such quantities as to insure a content in the finished steel of more than .05 per cent sulfur or selenium, or if both are used a total in excess of .05 per cent is usually required.

In the prior art, it has been suggested that from .50 to 2 per cent lead might be incorporated in a ferrous alloy containing from to 30 per cent of chromium for the purpose of reducing the size of the grains and grain boundaries and for preventing grain growth where the alloys are to be subjected to relatively high temperatures and subsequent cooling and for the purpose of rendering the alloy more workable and more resistant to corrosion. However, it has apparently not been conceived that the machinability of alloy steels could be improved by the addition of lead thereto.

This application is a continuation in part of my application Serial No. 208,069, filed May 14, 1938, which is a continuation in part of my application, Serial No. 177,292, filed November 30, 1937.

My invention contemplates the use of 'small percentages of lead in alloy steels. It contemplates the use of lead in such steels in amounts of .03 to 1.00 per cent, although it is believed that steels containing from .03 to .50 per cent of lead are preferable. It further involves the introduction of the lead into the steels in such a manner that it will be retainedtherein mainly in submicroscopic form comparatively uniformly dispersed throughout the steel.

My invention is applicable to the so-called nickel steels wherein the carbon may range from .10 to .60 per cent, the manganese from .10 to 1.00 per cent, the silicon from traces to 0.50 per cent, the phosphorus from traces to .05 per cent, 5 the sulfur from traces to .06 per cent and the nickel from .40 to 6.00 per cent. It is also applicable to the "nickel-chromium steels wherein the carbon ranges from .10 to .60 per cent, the manganese from .10 to 1.00 per cent, the silicon 10 from traces to 0.50 per cent, the phosphorus from traces to .05 per cent, the sulfur from traces to .06 per cent, the nickel from 1.00 to 4.00 per cent and the chromium from .40 to 2.00 per cent. Likewise, it is applicable to' the molybdenum 15 steels wherein the carbon ranges from .10 to .60 per cent, the manganese from .10 to 1.00 per cent, the silicon from traces to .50 per cent, the phosphorus from traces to .05 per cent, the sulfur from traces to .06 per cent, the chromium from traces to,1.25 per cent, the nickel from traces to 4.00 per cent and the molybdenum from .10 to .50 per cent.

My invention is also applicable to the chr0 mium steels wherein the carbon ranges from .10 to.1.l0 per cent, the manganese from .10 to 1.0 per cent, the silicon from traces to .50 per cent, the phosphorus from traces to .05 per cent, the sulfur from traces to .06 per cent, and the chromium from .25 to 2.00 per cent. It is also applicable to the "chromium-vanadium steels wherein the carbon ranges from .10 to 1.00 per cent, the manganese from .10 to 1.00 per cent, the silicon from traces to .50 per cent, the phosphorus from traces to .05 per cent, the sulfur from traces to .06 per cent, the chromium from .50 to 1.50 per cent and the vanadium from .10 to .30 per cent. Likewise, it applies to the "manganese steels wherein the carbon ranges from .10 to .60 per cent, the manganese from 1.25 to 2.00 per cent, the silicon from traces to .50 per cent, the phosphorus from traces to .05 per cent and the sulfur from traces to .06 per cent.

In the pursuance of my development, lead has been added to the steel by a number of ,methods which will be discussed more in detail hereinafter. At this point, it will suflice to say that it seems to be important that the lead be added to the steel in subdivided form and under conditions wherein considerable agitation of the steel is occurring. For example, lead has been successfully dispersed throughout the steel by introducing it into molten steel in a crucible in a high frequency induction furnace which naturally causes an agitation of the steel. It has also been successfully dispersed throughout the steel mold. It is also important that the lea-d be introduced in quantities sufllcient to insure that the amount desired is retained in the steel. For example. my tests show that the introduction of cut of! bars of S. A. E. 1020, the steels without lead, and the steels of my invention. By dividing the average time required to cut off bars of the steels of my invention by the time required to cut oil bars 01' S. A. E. 1020, I arrived at a ratio which I designate as the sawability index." Some results of these tests are shown in Table I.

'IAsu: l.-Compo|ition and suitability ifldicu ofezperimental low sulfur steels showing 017cc! 0/ lead Composition Brinell Host No. Heat treatment hard zrgi 0 Mn P s s1 01' Ni Mo Pb .10 .54 .024 .oes .000 Norm. moon 114 .93 .17 .85 .025 .035 .114 .d0 121 .73 .47 .7 .027 .025 .088 NOl'lll. 1500 F 179 .68 .46 .80 .02 .025 .170 do.... 179 .51 .88 .7 .022 .014 .164 Norm. 1450 F 269 .72 .88 .83 .083 .025 .152 d0 277 .56

lead in percentages approximating 1 per cent by weight of the steel may result in a recovery of about .50 to .70 per cent lead under favorable conditions.

I have found that alloy steels containing lead within the range of .03 to 1.00 per cent have improved .machinability in various heat treated conditions and as produced by hot rolling. By this is meant that the said alloy steels 01' otherwise the same chemical composition when heat treated to the same strength and hardness are more easily machinable and can be machined at a greater rate of speed when they contain lead in the range of .03 to 1.00 per cent than when they do not contain this element. I have also found that in steels of essentially the same chemical composition, except for the lead content, those containing lead can be machined under commercial and economical conditions when they have higher hardness and higher strength if the lead is present than when the leadis absent.

Experience has shown that the addition of lead to the said alloy steels within the ranges indicated above does not harmfully afiect the forging and rolling characteristics; that said steels may be heat treated by the usual commercial methods; that the resulting heat treated steels have essentially the same mechanical properties, such as yield strength, tensile strength, elongation, reduction of area, impact resistance and hardness as the same steels without lead. 7

As indicated above, the use of lead to improve the machinability of steels is applicable to steels of different carbon contents. This relation is illustrated by steels oi. the type known as plain carbon steels in which the carbon content ranges from about .15 to .88 per cent; all of the steels being tested in the normalized condition. These steels were tested for their machinability by sawing tests in which the steels of my invention and steels of the same composition without lead were compared with a steel of the type designated as It will be noted that the sawabality indices of the lead-containing steels, Heats Nos. 3495, 3497 and 3499, are decidedly lower than the comparison steel of essentially the same chemical composition but containing no lead. These outstanding improvements in machinability were effected by lead contents of less than .20 per cent and in steels of hardnesses of the range of about to about 270 on the Brinell scale.

The beneficial effect on the machinability, resulting from the practice of my invention with alloy steels, is illustrated by the data shown in Table II, in which I have used an alloy steel containing the special alloying elements chromium, nickel and molybdenum and have used this steel with and without additions of lead. This steel is rather close to the specified composition for the S. A. E. steels designated as S. A. E. 4340 and X-4340.

The results of sawability tests are shown for these alloy steels after the specimens had been given two heat treatments such as would be used in commercial practice; In the first heat treatment, specimens were heated to 1500 F. quenched in oil and then drawn or tempered at 1000 F. to produce a, Brinell hardness of 341. In the second heat treatment, specimens were annealed at 1500 F. and then tempered or drawn at 1250 F., to produce a Brinell hardness of 210. Sawability tests showed conclusively that the leadcontaining specimens had better machinability. For example, when these steels were tested at a Brinell hardness of 341, it required about 26 per cent longer time to cut off the bars which did not contain the lead. When the bars were tested at a hardness of 210 Brinell it-required 16 per cent longer time to cut off the bars which did not contain the lead.

In addition to the steels of my invention showing greater machinability in saw tests they will, in general, make it possible to increase both speeds and feeds in the ordinary machining operation. This eiTects an additional saving in the 4 amount of time required to do a given amount S. A. E. 1020. In making the sawing tests, comparison was made between the time required to of work, or, stated another way, increases the amount of production per machine man hour.

TABLE II.- Ejfect of lead on the machinabilitu of Cr- Ni- IvIo steels Composition Saw- Heat N 0 Heat treatment 2E32 ability 0 Mn r e si Gr Ni Mo Pb W .48 .74 .022 .017 .144 .72 1.42 .16 Oil uench from 1500 F. draw 1000 F 341 .73 .49 .77 .024 .016 .160 .75 1.84 .17 .158 o 341 .58 .48 74 022 017 144 72 l. 42 l6 Annealed from 1500 F. draw 1250 F. 210 64 .49 .77 .024 .015 .150 1.84 .17 .168 -do 210 .55

In the production of my alloy steels Ido not rely upon high percentages of chromium or on the presence of molybdenum to. put theleadin solid solution and my invention can be applied to alloy steels in which chromium and molybdenum are not present. In fact, my present application as well as my applications, Serial No. 208,069 and Serial No. 177,292, reveal the introduction of lead into plain carbon steels for the purpose of improving the machinability.

In the practice of my invention two classes of alloying elements areemployed, namely, ferrite strengtheners such as nickel, copper, silicon and cobalt and carbide formers such as chromium. molybdenum, tungsten and vanadium. Manganese is also a desirable alloying element and may be said to belong to both of the above classescertain objectionable effects of phosphorus its wise serve as grain refining elements.

use as an alloying element is somewhat limited. The elements zirconium, tantalum and columbium also function as carbide formers and likepurpose of this application, they may be classed as carbide formers. Thus the alloy steels which are responsive to my method of improving their machinability will have as their alloying elements metals selected from the group of ferrite strengtheners or the carbide formers or a combination of metals selected from these two groups. For example, in the nickel alloy steels (S. A. E. 2000, 2100, 2300 and 2500) the nickel is a ferrite strengthener although it has otherfunctions in alloy steels. In the chromium steel (8. A. E. 5100) the chromium is a strong carbide former although it has other functions in alloy steels.

. In the nickel-chromium steels (S. A. E. 3100,

3200, 3300 and 3400), use is made of both a ferm4 rite strengthening metal and a carbide forming metal and there are certain advantages which result from such combinations. In the chromium-vanadium steel (S. A. E. 6100) use is made of two carbide forming metals. It will be understeel and are in part dissolved in the ferrite. Therefore, the term strength-giving alloying metals which appears in the claims is intended to include carbide formers as well as ferrite strengtheners. I

In the composition cited in Table II,- use has been made of one ferrite strengthening metal and two carbide forming metals. It has been shown that, for many purposes and to some extent, one ferrite strengthener may be substituted for another and likewise one carbide former may be substituted for another without greatlymodifying the serviceability oi the resulting alloy steel.

The choice of ferrite strengtheners or carbide formers, or combinations of these, depends'in part upon fabrication requirements and the .intended use of the alloy steels. Cost of the alloying elements is also a factor which has to be given consideration. Ferrite strengtheners, as a class, are used to enhance toughness and cold formability while carbide formers favor increased hardness and resistance to wear. These relations may not hold for all ranges in compositions, however. The general principle used in selecting alloying elements for making alloy steels is For the in an alloy containing carbon within the range of .07 to .25 per cent, manganese from .30 to .70 per cent, silicon from traces to .30 per cent, phosphorus from .10 to .15 per cent. sulfur from traces to .06 per cent, copper from .75 to 1.25 per cent and nickel from .40 to .70 per cent. Though alloys of this type are frequently used under conditions where machining is not required, there are occasions when machining is desirable and such an alloy containing lead is within the scope of my invention. I

In the course of the development of my invention I have prepared numerous heats of steels other than those previously enumerated. Some of these are set forth in Table 111.

Table III.-E:cp ri mental alloy steels with and without lead (100# split heats) Chemical comp0siti0n-percent Heat 0 Mn 31 s 2 Ni 01- Mo Pb These heats were prepared in a high frequency induction furnace. Then, half of the steel was poured into an ingot mold, whereupon lead in finely divided form was added to the molten steel remaining in the furnace. After a short interval of time during which the steel was agitated by the induced current, the lead-containing steel was poured into a second ingot mold. The resulting 50 lb. ingots were forged and rolled into bars. About half of each ingot was rolled. into one inch round bars and the other half into inch round bars. No noticeable diflerence was observed between the lead-free and the leadcontaining steels in the forging and rolling operations. The compositions given in Table III are the results of chemical analyses taken from said ingots. Steels of the type listed in Table III are also within the scope of my invention.

Another illustration of the advantages of additions of lead to improve the machinability of alloy steel is provided by a steel containing about 1.00

per cent carbon, .90 per cent manganese, .30 per cent silicon, .025 per cent sulfur, .025 per cent phosphorus, :12 per cent molybdenum and .18 per cent lead. This steel was drawn into wires of .060 and .030 inch diameter and used in the production of small watchparts in automatic machines.

afound to have good machinability-and to be superior in this respect to similar steels not conformers ,or either of them and also containing a taining lead.

My invention is also applicable to that type of steel containing constituents designed to aid in controlling the grain size of the steel. Thus, it is within the scope of my'invention to embody from .03 to 1.00 per cent lead in a steel containing from effective'amounts to 1.70 per cent carbon together with ferrite strengthening elements and carbide grain defining element such as aluminum or titanium in the amounts of one-half to six pounds per ton.

The use of lead in alloy steels to improve their machinability does not require increasing the sulfur content of these steels above normal specifications although for certain purposes further improvement in machinability may be effected by slightly increasing the sulfur content. This, however, is only permissible in certain parts where the increased sulfur content does not harmfully afiect themechanical properties 'or where the desired mechanical properties can be obtained by heat treatment.

It will be seen from the above that my invention results in certain important advantageous characteristics in alloy steels. In the first place, my invention results in marked improvement in machinability of alloy steels of the type described. In addition, there is an improvement in the grain structure of such steels. Furthermore, these steels containing lead possess lower frictional resistance or coeflicients of friction than other steels of otherwise similar compositions but not containing lead. Other advantages will appear from the previous description and the appended claims.

Having thus described my invention, what I claim is 1. An alloy steel of the class containing strength-giving alloying metals in proportions within the range of 0.50 to 6.00 per cent, and characterized by good machining properties, said steel consisting essentially of said alloying metals within the range specified, carbon in effective amounts up to 1.70 per cent, silicon from a trace to 2.50 per cent, phosphorus from a trace to 0.15 per cent,

sulfur from a trace to 0.30 per cent, lead iithe range between 0.03 and 1.00 per cent, and .the balance being substantially all iron, at least a .major portion of the lead being uniformly dispersed throughout the steel and serving to improve the machinability thereof.

2. An alloy steel of theclass containing strength-giving alloying metals in proportions within the range of 0.50 to 6.00 per cent, and characterized by good machining properties, said steel consisting essentially of said alloying metals within the range specified, carbon in effective amounts up to 1.70 per cent, silicon from a trace to 2.50 per cent, phosphorus from a trace to 0.15 per cent, sulfur from a trace to 0.30 per cent, lead in the range between 0.03 to .478 per cent, and the balance being substantially all iron, at least a major portion of the lead being uniformly. dispersed throughout the steel and serving to improve the machinability thereof.

3. An alloy steel of the class containing strength-giving alloying metals in proportions within the range of 0.50 to 6.00 per cent, and characterized by good machining properties, said steel consisting essentially of said alloying-metals within the range specified, carbon in effective amounts up to 1.70 per cent, silicon from a trace to 2.50 per cent, phosphorus-from a trace to 0.15 per cent, sulfur from a trace to 0.06 per cent, lead in the range between 0.03 to 1.00 percent, and the balance being substantially all iron, at least a major portion of the lead being uniformly dispersed throughout the steel and serving to improve the machinability thereof.

4. An alloy steel of the class containing strength-giving alloying metals in proportions within the range of 0.50 to6.00 per cent, and characterized by good machining properties, said steel consisting essentially of said alloying metals within the range specified, carbon in effective amounts up to 0.60 per cent, silicon from a trace to 2.50 per cent, phosphorus from a trace to 0.15 per cent, sulfur from a trace to 0.30 per cent, lead in the range between 0.03 to 1.00 per cent, and the balance being substantially all iron, at least a major portion of the lead being uniformly dispersed throughoutthe steel and serving to improve the machinability thereof.

5. An alloy steel of the class containing strength-giving alloying metals in proportions within the range of 0.50 to 6.00 per cent,'and characterized by good machining properties, said steel consisting essentially of said allowing metals within the range specified, carbon in effective amounts'up to 1.70 per cent, silicon from a trace to 2.50 per cent, phosphorus from a-trace to 0.05 per cent, sulfur from a trace to 0.06 per cent, lead in the range between 0.03 to .478 per cent, and the balance being substantially all iron, at least a major portion of the lead being uniformly dispersed throughout the steel and serving to improve the machinability thereof.

6. An alloy steel of the class containing strength-giving alloying metals in proportions within the range of 0.50 to 6.00 per cent, and characterized by goodmachining properties, said steel consisting essentially of said allowing metals,

within the range specified, carbon in effective .50 per cent, phosphorus from a trace to 0.05 per cent, sulfur from a trace to .06 per cent, lead in amounts up to .60 per cent, silicon from traces to PatentNo. 2,182,759.

CERTIFICATE OF CORRECTION.

I December 5, 1939.

OSCAR E. HARDER.

It is hereby certified that error appears "in the printed specification of the above numbered patent requiri correction as follows: Pege 1 first column, line 56, for the word "defining" read refining; and second column, lines 50 and. 6b., claims 5 and 6 respectively, for "ellowing" read alloying;

and that the said Letters Patent shouldbe read with this correction therein that the same may conform to the record of the cese in the Patent Office.

Signed and sealed this 6th day of February, A. D. 19MB.

Henry Van Arsdale,

(Seal) Acting Commissioner of Patents. 

